Look at the BIOS parameters before boot, there should be an option to enable/disable the Usb EHCI (enhanced host control interface). As far as I understand it is enabled by default, but a previous user may have disabled it.

You can obtain basic diagnostic information from the Windows event log, and since you have access to an oscilloscope you might want to try a tool for Usb electrical analysis (see http://www.usb.org/developers/tools/).

This is a laptop, I have very limited options. There is no EHCI option in BIOS.

I would go back to my previous suggestion to burn a linux OS on a DVD or pen drive (if the PC can boot from a Usb pen drive). lubuntu.net is relatively lightweight and should work with acceptable performance.